APPARATUS AND METHOD FOR HANDLING PAGE PROTECTION FAULTS IN A COMPUTING SYSTEM

• US 20200133888A1
• Filed: 12/16/2019
• Published: 04/30/2020
• Est. Priority Date: 07/29/2008
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Murray, Simon, North, Geraint M.
• Granted Patent: US 11,119,949 B2
• Time in Patent Office: Days
• CPC Class Codes: G06F 12/10 Address translation
• CPC Class Codes: G06F 12/1009 using page tables, e.g. page table structures
• CPC Class Codes: G06F 12/12 Replacement control
• CPC Class Codes: G06F 12/145 the protection being virtual, e.g. for virtual blocks or segments before a translation mechanism
• CPC Class Codes: G06F 12/1483 using an access-table, e.g. matrix or list
• CPC Class Codes: G06F 2212/1052 Security improvement
• CPC Class Codes: G06F 8/52 Binary to binary
• CPC Class Codes: G06F 9/4552 Involving translation to a different instruction set architecture, e.g. just-in-time translation in a JVM
• CPC Class Codes: G06F 9/45537 Provision of facilities of other operating environments, e.g. WINE I/O emulation G06F13/105

Abstract

Method and apparatus for handling page protection faults in combination particularly with the dynamic conversion of binary code executable by a one computing platform into binary code executed instead by another computing platform. In one exemplary aspect, a page protection fault handling unit is used to detect memory accesses, to check page protection information relevant to the detected access by examining the contents of a page descriptor store, and to selectively allow the access or pass on page protection fault information in accordance with the page protection information.

Claims

1. A method of handling page protection faults, comprising:

converting a subject code executable that comprises a reference to at least one subject memory page having associated subject page access permissions into a target code executable by at least one target processor and including references to a target memory, the conversion including establishing a page descriptor store according to the reference to the subject memory page and the associated subject page permissions, and selecting address bits defining addresses of the plurality of memory locations based on information in the page descriptor store according to the subject page access attributes, and indicating a page protection condition of a corresponding subject memory page based on the values of the address bits; and

allowing an attempt to access the target memory location to proceed without an interruption in control flow if the attempted access is within the scope of the subject page access attributes for the associated subject memory page.

2. The method of claim 1, further comprising determining whether an attempt to access a target memory location within the plurality of memory locations crosses a subject page boundary, and allowing the attempt to proceed without interruption in control flow when the attempted access is within the permissions of all the subject pages involved in the attempted access.

3. The method of claim 1, further comprising setting up, in the target memory, a guard representation of the at least one subject memory page, the guard representation resident in an address space in the target memory that is identifiable by the target processor unit as inaccessible.

4. The method of claim 3, further comprising attempting to access either the target memory location within the plurality of memory locations or the guard representation in accordance with the information in the page descriptor store.

5. The method of claim 3, further comprising generating an exception in response to an attempt to access the guard representation.

6. The method of claim 1, further comprising associating the plurality of memory locations in the target memory with information inserted into the page descriptor store to enable redirecting attempted accesses to shared subject pages to a corresponding shared region within the target memory.

7. The method of claim 1, further comprising determining whether an attempt to access a target memory location within the plurality of memory locations crosses a subject page boundary, and allowing the attempt to proceed without interruption in control flow when the attempted access is within the permissions of the first subject page involved in the attempted access, and the permissions of the second subject page involved in the attempted access match those of the first subject page.

8. A computing system, comprising:

a translator unit arranged to convert a subject code into a target code, the subject code including a reference to at least one subject memory page having associated subject page access permissions;

a target processor unit arranged to execute the target code;

a target memory associated with the target processor unit and including a page descriptor store and plurality of memory locations related to the subject memory pages, the page descriptor store including alignment checking data, the alignment checking data indicating whether an attempt to access a target memory location crosses a subject page boundary; and

wherein the translator unit is arranged to allow an attempt to access the target memory location that crosses the subject page boundary to proceed without an interruption in control flow when the attempted access is within the permissions of all the subject pages involved in the attempted access.

9. The computing system of claim 8, wherein the page descriptor store is populated in response to system calls in the subject code that modify memory layout.

10. The computing system of claim 8, wherein the translator unit is configured to:

calculate the alignment checking data in response to the attempted access; and

store the alignment checking data in the descriptor store.

11. The computing system of claim 8, wherein the translator unit is configured to set up, in the target memory, a guard representation of the at least one subject memory page, the guard representation resident in an address space in the target memory that is identifiable by the target processor unit as inaccessible.

12. The computing system of claim 8, wherein the translator unit is configured to generate the alignment checking data based on a size of a page the subject memory page, a size of the subject memory access, and a start address of the subject memory access.

13. The computing system of claim 8, wherein the alignment checking data comprises a cross-page permission change flag, the cross-page permission change flag based on a comparison of access permissions across the subject page boundary.

14. A non-transitory computer readable medium having instructions recorded thereon which when executed by a computing system having at least one target processor cause the computing system to perform a process comprising:

converting a subject code executable that comprises a reference to at least one subject memory page having associated subject page access permissions into a target code executable by at least one target processor and including references to a target memory, the conversion including establishing a page descriptor store according to the reference to the subject memory page and the associated subject page permissions, wherein the page descriptor store includes alignment checking data, the alignment checking data indicating whether an attempt to access a target memory location crosses a subject page boundary; and

allowing an attempt to access the target memory location that crosses the subject page boundary to proceed without an interruption in control flow when the attempted access is within the permissions of all the subject pages involved in the attempted access.

15. The computer readable medium of claim 14, having instructions recorded thereon which when executed perform the further process of populating the page descriptor store in response to system calls in the subject code that modify memory layout.

16. The computer readable medium of claim 14, having instructions recorded thereon which when executed perform the further process of:

calculating the alignment checking data in response to the attempted access; and

storing the alignment checking data in the descriptor store.

17. The computer readable medium of claim 14, having instructions recorded thereon which when executed perform the further process of setting up, in the target memory, a guard representation of the at least one subject memory page, said guard representation resident in an address space in the target memory that is identifiable by the target processor unit as inaccessible.

18. The computer readable medium of claim 14, having instructions recorded thereon which when executed perform the further process of generating the alignment checking data based on a size of a page the subject memory page, a size of the subject memory access, and a start address of the subject memory access.

19. The computer readable medium of claim 14, having instructions recorded thereon which when executed perform the further process of creating the alignment checking data to include a cross-page permission change flag, the cross-page permission change flag based on a comparison of access permissions across the subject page boundary.